Status and conservation of Eastern Hoolock Gibbon Hoolock leuconedys in Assam, India

Rekha Chetry ¹, Dilip Chetry ²& P.C.Bhattacharjee ³

¹ Department of Zoology, Jawaharlal Nehru College, Boko, Kamrup, Assam 781123, India

^1,2,3 Gibbon Conservation Centre, Gibbon Wildlife Sanctuary, Mariani, Jorhat, Assam 785634, India

² Aaranyak, 50, Samanway Path, Survey, Beltola, Guwahati, Assam 781028, India

³ Department of Zoology, Gauhati University, Guwahati, Assam 7810014, India

Email: ¹ chetryrekha@gmail.com (corresponding author), ² dilip@aaranyak.org, ³ bhattapc@sify.com

Date of publication (online): 26 October 2012

Date of publication (print): 26 October 2012

ISSN 0974-7907 (online) | 0974-7893 (print)

Editor:Mewa Singh

Manuscript details:

Ms # o3073

Received 19 January 2012

Final received 15 May 2012

Finally accepted 16 August 2012

Citation: Chetry, R., D. Chetry & P.C. Bhattacharjee (2012). Status and conservation of Eastern Hoolock Gibbon Hoolock leuconedys in Assam, India. Journal of Threatened Taxa 4(13): 3183–3189.

Copyright: © Rekha Chetry, Dilip Chetry & P.C.Bhattacharjee 2012. Creative Commons Attribution 3.0 Unported License. JoTT allows unrestricted use of this article in any medium for non-profit purposes, reproduction and distribution by providing adequate credit to the authors and the source of publication.

Author Details: Rekha Chetry‘s research interest is on primate behaviour, ecology, and conservation biology. She has conducted several field studies on endangered primates of northeastern India. The corresponding author is an Assisstant Professor.

Dilip Chetry worked since 1994 in the field study of primate in northeastern India. He has particular interest in ecology, behaviour, conservationof primate and in community based conservation of biodiversity. He is Programme Head, Primate Conservation Division, Aaranyak and also Executive Director of Gibbon Conservation Centre, Assam, India.

Parimal Chandra Bhattacharjee’s research focus on ecology, ornithology, primatology and biodiversity conservation. He is former Head & Professor, Department of Zoology, Gauhati University, Assam, India

Author Contributions: RC and DC collected the data in the field. PCB assisted in writing of manuscript.

Acknowledgements: This report is based on work sponsored by Primate Conservation Inc. We are grateful to Noel Rowe for his generous support. We acknowledge our gratitude to Assam Forest Department, Government of Assam for providing us the necessary permission for conducting the survey and other logistical support. Thanks are due to the staff of Sadiya Forest Range specially Mr. Amarendra Pathak, Mr. Susen Koch, Mr. Rabi Gohain, and Mr. Thapa. We are also most grateful to Prof. Colin Groves, Prof. Warren.Y. Brokelman and Prof. Thomas Geissmann for helping us to identify the gibbons. We thank: Mr. Lalit Saikia and Mr. Pradip Baruah who assisted us in the field; Mr. Dimbeswar Chutia, Mr. Raju Lahan and Shambu Bauri who guided us in the forest. Special thanks go to Prof. David J. Chivers for going through the manuscript with valuable inputs and corrections.

Abstract: A field survey was conducted in 2010 from March to May in the reserve forests of Sadiya sub-division, in the Tinsukia District of Assam, India, to investigate the status of the Hoolock Gibbon. The data were collected using modified line-transect and call-count methods. We recorded 10 groups of gibbons in three reserve forests, through direct sighting. Of the 33 individuals recorded through direct sighting 63.6% were adults, 21.2% juveniles and 15.2% infants. The average group size of the sighted groups was 3.3 individuals, with an adult sex ratio of 1:1.1. We also recorded 10 groups of Rhesus Macaques in the area. Anthropogenic pressures included encroachment, felling of trees and inadequate infrastructure, and these were the major threats for Hoolock Gibbon and other wildlife in the region. Notably, the gibbons of Sadiya have been identified as the Eastern Hoolock Gibbon Hoolock leuconedys and this is the first report of the species from Assam.

Keywords: Conservation, Eastern Hoolock Gibbon, Hoolock leuconedys, Sadiya, status, threat.

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INTRODUCTION

Assam, one of the seven states in northeastern India, supports a rich biodiversity, with primates forming an important component. Out of the 25 species of non-human primates in India, nine species—Slow LorisNycticebus bengalensis, Rhesus Macaque Macaca mulatta, Assamese Macaque Macaca assamensis, Pig-tailed Macaque Macaca leonina, Stump-tailed Macaque Macaca arctoides, Capped Langur Trachypithecus pileatus, Golden Langur Trachypithecus geei, Phayre’s Langur Trachypithecus phayrei and Western Hoolock Gibbon Hoolock hoolock—are present in Assam. The Western Hoolock Gibbon is so far the sole ape recorded from Assam. Several studies have already been carried out on the status and distribution of Hoolock Gibbon in Assam (Mohnot 1995–2001; Das et al. 2005; Chetry et al. 2007; Choudhury 2006, 2009; Kakati et al. 2009). Sadiya is a subdivision of Tinsukia District of Assam and it is the extreme eastern boundary of the state. Administratively, Sadiya is a part of Assam, yet the area has no land connection with any other part of the state, and the landmass of Sadiya is continuous with the Lower Dibang Valley District of neighbouring Arunachal Pradesh. There are six reserve forests in the subdivision of Sadiya range of Doomdooma Forest Division of eastern Assam circle. The reserve forests are Hallowgaon, Kukuramara, Kundil Kalia, Sadiya West Block and Sadiya North Block, covering 125.12km² of forest. Studies were carried out from time to time to understand the primate diversity of the state, including Sadiya. The Indo-US Primate project first did an extensive primate survey in Sadiya range during 1994 (Mohnot 1995–2001), followed by another survey of primates in Sadiya (Sharma & Sinha 2007). Western Hoolock Gibbon occurred in the area in each study, but the unique geographic location of the area stimulated us to give a second thought about the identity of the gibbons of Sadiya. Discovery of the Eastern Hoolock Gibbon H. leuconedys in the Mehao Wildlife Sanctuary, and its adjacent Kornu Reserve Forest in Arunachal Pradesh (Chetry et al. 2007, 2008, 2010; Chetry 2009) also made us reconsider the identity of the gibbons of Sadiya. Considering the land continuity of Sadiya with the Lower Dibang Valley District of Arunachal Pradesh, we hypothesised those gibbons of Sadiya to be Eastern Hoolock. Hence, to verify our hypothesis, we carried out a fresh survey of Hoolock Gibbons in the Sadiya area, after we confirmed here, for the first time, the occurrence of Eastern Hoolock Gibbon in Sadiya and, for that matter, in Assam (Chetry & Chetry 2010) (Image 1). We also report the anthropogenic pressures on the species and its habitats, so that effective conservation measures can be developed for Eastern Hoolock Gibbon in the study area in future.

MATERIALS AND METHODS

The Sadiya subdivision is located at 95⁰40’1’’E & 27⁰45’02’’N, covering an area of 789.95km² (Image 2). We conducted a field survey in 2010 from March to May in the reserve forests of Sadiya sub-division, in the Tinsukia District of Assam, India. The topography is a flat plain, gradually sloping from north to south. The vegetation in this area has been described as Assam valley tropical wet evergreen forest (Champion & Seth 1968). The forests in the study area have an upper canopy of Michelia champaca, Shorea  assamica, Terminalia myriocarpa. The middle canopy is mostly dominated by Vatica  lanceaefoliaand Mesua ferrea, along with Bombax ceiba, Terminalia belerica, Canarium resinifesum, Terminalia chebula, Eugenia jambolana, Sapium  baccatum, Dillenia  indica and Bischofia  javanica. 

(i) Direct method

We followed modified line transect method (Burnham et al. 1980; NRC 1981) for the survey, depending on the habitat and the forest condition. We laid the transects in a stratified random manner to cover all representative areas of the park (Mueller-Dombois et al. 1974; Kent et al. 1994). The total length of the transects was 212km. Three observers walked randomly through existing forest trails and occasionally forest tracts without trails covering an average of 10–12 km/day. We initiated the walk transects in the morning (0600h) and terminated in the evening (1500h). The observers walked slowly along the transect pausing at regular intervals of 500m. On sighting the gibbon, we recorded the GPS (Global Positioning System) location, the group structure and individual details, such as age, sex and number of individuals. At 500m intervals, and at each location where the gibbon was encountered, the observers estimated tree height and canopy cover within an area of 10m radius and also took note of the evidence and degree of grazing and logging in the study area.

(ii) Indirect method

A. Call-count method: This involved recording hoolock gibbon calls. Whenever calls were heard in the absence of sightings, the distance of the call was estimated and recorded along with time, direction, duration and GPS co-ordinates of the observers.

B. We also recorded some secondary information relevant to the study, such as information about hunting and traditional beliefs, through informal interaction with forest field staff, local guides and elderly people.

RESULTS

Population status

For the first time the occurrence of Eastern Hoolock Gibbon from the Sadiya subdivision of Assam is reported. A total of 32 individuals in 10 groups were recorded, based on direct sighting from three reserve forests in Sadiya (Table 1). Again, based on call count, the occurrence of another 16 groups was estimated (Table 2, Image 3).

Population distribution

The survey covered 212km of transects in various parts of the reserve forests and hoolock gibbons were found within an altitudinal range of 100–176 m.

Group size and age composition

The group structure and composition of the sighted groups are shown in Table 1. The average group size was three with individuals ranging from 1 to 5. Most of the groups were observed with either 2 (4 groups) or 4 (2 groups) individuals. The adult sex ratio was 1:1.1. Age classification shows that, of the total sighted population, 63.6% were adults, 21.2% juveniles and 15.2% infants.

Sighting time and call time

Of the 10 groups sighted directly, sighting time of all groups (10 groups) was before 1200h. All gibbon calls were recorded before 1200h, of average duration 15.25 minutes, with a range between 10–25 minutes.

Primate diversity of Sadiya

During the survey period we recorded the occurrence of only Rhesus Macaque Macaca mulatta besides the Eastern Hoolock Gibbon in Sadiya. We sighted 120 Rhesus Macaques in 10 groups.

Local extinction of hoolock gibbon

We interacted with the local people of all six reserve forests to know about the past status of gibbons in the areas. All these interactions have led us to conclude that gibbons were common in all forests of Sadiya in the past. Only 50 years ago all the reserve forests had populations of gibbons, but at present there are no gibbons in any of them (Table 3). This indicates that the species has become locally extinct from these three reserve forests. It has been assumed that about 40–45 years ago the species was wiped out by large-scale clearing of forest for human settlement and agricultural practice.

Threats

During the survey we also tried to identify the threats for hoolock gibbon and other wildlife of the area. Based on our observation we have identified the following threats:

Status of the forest: It is evident that Eastern Hoolock Gibbon occurs in the reserve forests of Sadiya. Reserve forests, unlike sanctuaries or national parks, do not enjoy strong legal protection. Additionally, this status makes the reserve forests more vulnerable to various types of exploitation.

Hunting: There was no direct evidence of hunting, but indirect information supports the occurrence of the hunting of hoolock gibbon and other wildlife in Sadiya.

Encroachment: Massive encroachment of forestland for human settlement and for agricultural activities was observed during the survey. A total of 60.70km² of forestland is under encroachment out of 125.12km² (Table 3).

Selective logging: Illegal felling of selective trees, such as Uriam Bischoffia javanica, Simalu Bombax ceiba, Halak, Tita sopa Michelia champaca, was also observed during the survey.

Collection of non-timber forest products: Extraction of non-timber products, such as cane, bamboo and medicinal plants, is a common practice among the local community. Cane Calamusspp., bamboo Bambusa spp., Musa spp., fern species and Tora Alpiniaspp. are also extracted commercially from the forests.

Grazing pressure: There is high grazing pressure from the surrounding villages, as well as from the cattle farms.

Lack of awareness: Lack of awareness among the local community towards the conservation of wildlife in general, and the Eastern Hoolock Gibbon in particular, is a perennial problem.

Lack of patrol infrastructure: During the survey, we observed that there were neither staff quarters nor a forest department office in any reserve forest for monitoring or patrolling the forest. There are only eight forest staff in Sadiya subdivision to combat illegal activities in the forest.

DISCUSSION

The Eastern Hoolock Gibbon is reported for the first time from Assam, showing the extended distribution of the species in India. Earlier, Das et al. (2006) first reported Eastern Hoolock Gibbon from Lohit district of Arunachal Pradesh. Then, there was a report of Eastern Hoolock Gibbons from the lower Dibang Valley District of Arunachal Pradesh (Chetry et al. 2008; Chetry 2009; Chetry et al. 2010).

There were 26 groups of Eastern Hoolock Gibbons in three reserve forests, namely Halaugaon, Kukuramara and Kundil Kalia. With this finding, the Sadiya area is established as the single habitat pocket of Eastern Hoolock Gibbon in the state of Assam. According to Das et al. (2006), the average group size for the gibbon was 3.37, while Chetry et al. (2009) recorded an average group size of 3.14 in Mehao Wildlife Sanctuary. The average group size recorded in this study is 3.3. Variation in group size in different habitats may be due to the differences in the distribution, abundance and quality of food resources in the habitat. Regarding the altitudinal distribution range of the species, Groves (1971) reported that the Eastern Hoolock Gibbon is distributed at an altitude range of 1067–1219 m in Myanmar and China. Similarly, Das et al. (2006) recorded the species between 122–1075 m in Arunachal Pradesh. Again, Chetry et al. (2010) reported an altitude range of 142–1865 m in Mehao Wildlife Sanctuary in Lower Dibang Valley District of Arunachal Pradesh. In this study, it is shown that in Sadiya the Eastern Hoolock Gibbons are distributed between 100–176 m. This clearly shows that the species is distributed at much lower elevations than thought earlier. Simalu Bombax ceiba, Ajar Lagerstroemia speciosa, Halakh Terminalia myriocarpa and Lata jari Ficus maclellandii were the dominant vegetation in the reserve forests.

In addition to the Eastern Hoolock Gibbon, reserve forests in Sadiya support only one other species of primate - Macaca mulatta. Regarding other primates we neither had any direct sighting nor any secondary information. This indicates that Macaca assamensis, Trachypithecus pileatus, and Nycticebus bengalensis, along with Macaca arctoides and Macaca leonina, which are sympatric to the Eastern Hoolock Gibbon in other habitats, are absent in Sadiya. This absence of all these species, particularly Macaca assamensis, Trachypithecus pileatus, and Nycticebus bengalensis, is significant.

With the addition of the Eastern Hoolock Gibbon Hoolock leuconedys, the primate diversity of Assam has been increased by another species and this has undoubtedly made Assam, the Indian state with the highest primate diversity.

Habitat loss and fragmentation resulting from encroachment for settlements and agricultural practices are posing a major threat, not only to the Eastern Hoolock Gibbon but also to other wildlife in Sadiya. Habitat loss and fragmentation have already been identified as the principal threats to gibbons in the entire distribution range in northeastern India (Chetry et al. 2007). Sincere efforts for conservation, involving the local community with long-term vision, are required, along with population monitoring and ecological study of the Eastern Hoolock Gibbon. Viewing Sadiya as the only Eastern Hoolock Gibbon habitat in Assam, the state forest department should take immediate steps to conserve this population. The state government can notify all the three reserve forests with Eastern Hoolock Gibbons into a sanctuary to provide more legal protection to the species and its habitats.

REFERENCES

Burnham, K.P., D.R. Anderson & J.L. Laake (1980). Estimate of Density from Line Transect Sampling of Biological Populations. Wildlife Monograph No. 72. The Wildlife Society, Washington D.C., 202pp.

Champion, H.G. & K. Seth (1968). A Revised Survey of  Forest Types of  India. Government of India, Publication, New Delhi, xxvii+404pp.

Chetry, D. (2009). Conservation of Hoolock Gibbon by integrating field survey with education and awareness programme in Mehao Wildlife Sanctuary in Arunachal Pradesh, India. Final project report submitted to CEPF & ATREE, 44pp.

Chetry, D., R. Chetry, A. Das, C.Loma & J. Panor (2008). New Distribution records of Hoolock leuconedys in India. Primate Conservation23: 125–128.

Chetry, D., R. Chetry, K. Ghosh & A.K. Singh (2010). Status of Eastern Hoolock Gibbon (Hoolock leuconedys) population in Mehao Wildlife Sanctuary in Arunachal Pradesh, India. Primate Conservation 25: 87–94.

Chetry, D., R. Chetry & P.C. Bhattacharjee (2007). Hoolock: The Ape of India. Gibbon Conservation Centre Press, Assam, India, xii+133pp.

Chetry, R. & D. Chetry (2010). First distribution record of Eastern Hoolock Gibbon in Assam, India. Primate Conservation25: 95–97.

Choudhury, A.U. (2006). The Distribution and Status of Hoolock Gibbon, Hoolock hoolock, in Manipur, Meghalaya, Mizoram, and Nagaland in Northeast India. Primate Conservation 20: 79–87

Choudhury, A.U. (2009). The Distribution, Status and Conservation of Hoolock Gibbon, Hoolock hoolock, in Karbi Anglong District, Assam, Northeast India. Primate Conservation 24: 1–10.

Das, J., J. Biswas, P.C. Bhattacharjee & S.M. Mohnot (2006). First distribution records of the Eastern Hoolock Gibbon Hoolock hoolock leuconedys from India. Zoos’ Print Journal21(7): 2316–2320.

Das, J., P.C. Bhattacharjee, J. Biswas & D. Chetry (2005). Western Hoolock Gibbon: Socioecology, Threats and Conservation Action Plan. Department of Zoology, Gauhati University and Primate Research Centre, Northeast centre, Guwahati, India, 70pp.

Groves, C.P. (1971). Geographic and Individual variation in Bornean gibbons, with remarks on the systematics of the subgenus Hylobates. Folia Primatologica 14: 139–53.

Kakati, K., R. Raghavan, R. Chellam, Q. Qureshi & D.J. Chivers (2009). Status of Western Hoolock Gibbon (Hoolock hoolock) populations in fragmented forests of eastern Assam. Primate Conservation24: 127-137.

Kent, M. & P. Coker (1994). Vegetation Description and Analysis: - A practical Approach.John Wiley and Sons, Ltd., Chichester, 363pp.

Mohnot, S.M. (1995–2001). Indo-US Primate Project Report: Annual Report I, II, III, IV,V,VI. Department of Zoology, J.N.V. University, Jodhpur, Rajasthan, India.

Mueller-Dombois, D. & H. Ellenberg (1974). Aims and Methods of Vegetation Ecology. John Wiley and Sons, Inc., New York, 547pp.

National Research Council (1981). Techniques for the study of Primate Population Ecology. National Academy Press, Washington D.C., 227pp.

Sharma, N. & A. Sinha (2007). Survey and conservation status of non-human primates in reserve forest and proposed reserve forests of Eastern Assam Circle. Final Report to the Assam Forest Department.National Institute of Advanced studies, Bangalore, 57pp.